Oscillation generator



Nov. 3, 1942.

w. J. PocH OSCILLATIIQN GENERATOR Filed June 22, 1940 .E'XI'Efl/VJL 'SYNC. INPUT 7 Y 6 mil F'HOM E I EX'I'E'fl/VfiL SYNC 5a 44 FROM 60 MULT/ V/BRJTO Waldemar J ZSnuentor Pac Patented Nov. 3, 1942 OSCILLATION GENERATOR Waldemar J. Pooh, Collingswood, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application June 22, 1940, Serial No. 341,796

3 Claims. ,(Cl. 25036) This invention relates to television circuits and more particularly to control oscillators for use in television circuits.

In television systems employing cathode ray tubes, it is necessary to utilize electric pulses occurring at a comparatively high frequency for deflecting the cathode ray horizontally and other pulses occurring at a comparatively low framing frequency for deflecting the cathode ray vertically. It has been found preferable to generate the impulses by means of frequency divider circuits including electric discharge devices, or the like. The oscillator and associated circuits of this in- Vention may be advantageously used to generate master synchronizing pulses from which are derived the horizontal and vertical synchronizing pulses of a television transmitter.

In previously used master oscillators for generating synchronizing signal impulses, it is generally the practice to generate a frequency twice that of the line frequency or, in the case of 441 lines per frame, 26,460 cycles per second by providing a thermionic tube oscillator circuit having a plate circuit containing inductance and capacity whose resonant frequency is 26,460 cycles per second. In such known systems the master os- Relaxation oscillators of the type shown and I described by Abraham and Block in Ann. de

Physique XII, page 237, 1919 and Balth van der Pol. Jun., D. 30., page 978, London Philosophical Magazine, Journal of Science, volume 2, November 1926, comprises a plurality of triodes coupled by resistances and capacities only. In this well known system, which may be regarded as a multiple stage resistance-capacity coupled amplifier, the phase inverting properties of a thermionic tube furnish voltages to the input of the oscillator tube 180 degrees out of phase with the output and thus cause the oscillator tube to oscillate at a frequency dependent upon the values of resistance and capacity in the coupling circuit.

According to this invention, an L-type network is used to provide the necessary 180 phase shift between the oscillator tube output and input voltage to produce oscillations.

A further feature of the invention is the synchronizing of the output of the main oscillator with a voltage source whose frequency may be approximately 60 cycles per second. The broad frequency response of the oscillator herein disclosed is advantageous in that any variation in the external synchronizing frequency is readily followed by the oscillator.

The principal object of my invention is toprovide an oscillator whose frequency output may be controlled over a comparatively wide range of frequencies.

Another object of this invention is to provide an oscillator circuit having an auxiliary thermionic means for controlling its output frequency.

Other and incidental objects of the invention will be apparent to those skilled in the art from a reading of the following specification and an inspection of the accompanying drawing in which Figure 1 is a circuit diagram showing one form of this invention, and

Figure 2 is a similar diagram showing another form of this invention.

Referring to Fig. 1, any suitable oscillation generatin device, such as oscillator tube I, is shown having a cathode 2, a control electrode 3, and an anode 4. A positive anode potential is supplied by a direct current source through resistor 5. The anode 4 of the triod tube I is coupled to a low pass network made up of series resistances 6, l and 8, and parallel condensers 9, H) and H. Series resistances l2 and I3 terminate the network, and resistance I3 is provided with a variable contact which is connected to the control electrode 3 for producing an ad-' justable amount of feedback voltage to the control electrode 30f the oscillator tube 1 A negative grid bias voltage is provided for control electrode 3 through a voltage drop caused by plate tive starting times. The velocity of any one train through the filter is dependent upon the values of resistances and capacities chosen in constructing the filter circuit. In accordance with this invention, the values of resistances and capacities are chosen so that a train f alternating current and voltage having a predetermined frequency is so delayed in the network that the voltage appearing across the output resistances l2 and I3 is 180 out of phase with the voltage of the same train when it enters the filter through coupling condenser it. This causes the tube 1 to sustain oscillations at the frequency whose filter input and output voltages are 180 out of phase.

An auxiliary tube shown as triode H contains a cathode IS, a control electrode I9 and anode 20. This auxiliary tube I1 is connected across resistance 21, which is in series with a network capacity such as condenser 9. A change in the value of resistance 2! causes a change in the characteristic of the filter, resulting in a change in the natural oscillating frequency of the circuit. The impedance of tube I1 is in parallel with resistance 2!. A potentiometer 22 is connected between the cathode M of the auxiliary control tube I1 and a negative D. C. potential source. The impedance of auxiliary tube I1 is controlled by changing the negative grid bias potential with the potentiometer 22, and the function of this tube is to provide a change in the operating frequency of the oscillator. The same result may be effected by means of the resistor 23. An additional fixed negative potential is supp-lied to the control electrode l9 of the auxiliary tube H by the common cathode resistor I4 and bypass condenser 15.

An' external synchronizing voltage is impressed on the coupling network at any suitable point such as the junction between resistances 8 and I2. Although the impedance of the network to this external synchronizing pulse may be relatively low, the resistor and condenser components of the filter are so chosen as to provide a 180 phase shift for the synchronizing voltage harmonic at which the oscillator is to operate. The phase shift of the relatively low synchronizing frequency is not sufficient to cause the circuit to oscillate at the low frequency of external synchronizing pulses.

The type of filter network illustrated in Fig. l is of the low pass type. A filter of the high pass type can be substituted very conveniently, as illustrated in Fig. 2.

In Fig. 2 there is shown another form of this invention. The discharge device 24 takes the form of a thermionic tube having a cathode 25, a control electrode 26 and an anode 27. However, any of the well known discharge devices obviously may be substituted. The anode 21 is supplied with a D. C. potential through resistance 28. The network in this takes the form of an L-type high pass bypass filter composed of series cap-acitances 29, 3D, 31 and 32, and parallel resistances 33, 34, 35 and 36. The output of the filter is returned to the control electrode 26 of the tube 24, and the values of capacities and resistances are so chosen, as explained under the discussion of Fig. 1, that the alternating current voltage of the desired frequency is shifted by 180 degrees so that, as in Fig. 1, the voltage appearing on the control electrode 26 is 180 degrees out of phase with the voltage appearing across the anode resistor 28. This causes tube 24 to generate oscillations at that predetermined frequency.

Cathode resistor 31 and condenser 38 are used to provide a negative bias voltage on the control electrode 26 with respect to its cathode 25.

An auxiliary control tube 35 contains a cathode 40, control electrode 4!, and anode 42. The anode 42 of this auxiliary control tube -39 is conthrough resistance 5 i grosses nected in the network so that the impedance of the control tube 39 is in parallel with the resistance 33. This auxiliary tube can be connected parallel to any of the resistances 34, 35 and 36 to produce the desired regulation of the oscillator frequency. A change in the anode impedance of the tube 39 will cause a corresponding change in the resistance value contained in the network and therefore change the velocity of the train of alternating current voltage through the network so that an alternating current voltage train having another frequency will pass through the network at such a velocity that it will be delayed degrees, thus causing the oscillator circuit to generate oscillations at this other frequency. The output of the oscillation generator is preferably taken off at the anode 21 of tube 24.

The automatic frequency control means shown in Fig. 2 comprises two discharge devices 43 and 44 and a rectifier unit 45.

The voltage from an auxiliary synchronizing source is impressed upon the control electrode 46 of the discharge device 43 through coupling condenser 41. The control electrode 46 is supplied with a negative bias by cathode resistor 48 and filter condenser 49. The anode 50 of the tube 43 is supplied with a positive potential This results in an alternating current voltage across resistance 5| which takes the form and the frequency of the external synchronizing source impressed upon the control electrode 46.

A part of the voltage from the 60 cycle multivibrator in the impulse generator, of which tube 24 and its associated filter network is a part, is impressed upon the control electrode of the discharge device 44 through condenser 53. A negative bias is impressed upon control electrode 52 through cathode resistor 54 and its associated filter condenser 55. The anode 56 of the discharge device 44 is also supplied by a positive voltage source through resistor 5| so that there appears across resistor 5| a combination of alternating current voltages whose frequencies correspond to the external synchronizing frequency and the frequency of the 60 cycle multivibrator of the impulse generator. This resultant voltage is impressed upon the rectifier 45, which rectifies the impressed alternating current voltages resulting in a direct current voltage across resistor 51,

If the two frequencies are equal and their voltages out of phase by 180 degrees, there will be no'D. C. voltage across the circuit composed of resistor 57 and filter condenser 58 so that the only negative voltage bias on control electrode 4! of auxiliary control tube 39 will be that bias caused by the anode current voltage drop in Else common cathode resistor 31 and condenser If the two frequencies are equal and their voltages in phase, there will be impressed across the rectifier 45 an alternating'current voltage which will be rectified by rectifier 45 causing a negative voltage to appear across the resistor 51. This negative voltage in turn is impressed upon the control electrode of the auxiliary tube 39 in addition to the bias supplied by cathode resistor 31 so as to change the impedance of the auxiliary control tube 39 thus changing the impedance in the filter network and causing a corresponding frequency change as previously described.

When the oscillation generating circuit is ad justed to oscillate without a synchronizing control voltage at a frequency approximating 60 cycles, the addition of this synchronizing impulse by either of the methods shown in Figs. 1 and 2, the oscillator will tend to keep in step with the synchronizing voltage.

The detailed operation of the automatic frequency control circuit shown in Fig. 2 will be readily understood from the following illustration.

When this circuit is employed as a main oscillator of the impulse generator used to supply deflecting voltages for the cathode ray, a series of multivibrators divide the frequency to an output of 60 cycles per second. This multivibrator frequency of 60 cycles per second is impressed upon the control electrode 52 of tube 44, and the auxiliary synchronizing source voltage is impressed upon control electrode 46 of tube 43.

The voltage appearing across the resistor 51 and condenser 58 will stabilize at approximately one-half the bias voltage occurring when the alternating current voltages appearing across resistor are in phase. This will cause stabilization of the oscillation generator at a point where the auxiliary synchronizing voltage and the output from the 60 cycle multivibrator are equal in frequency, but displaced in phase by approximately 90 degrees, the voltage of the multivibrator lagging the voltage of the synchronizing source. It follows that any slight change in the 60 cycle multivibrator frequency from that of the auxiliary synchronizing source frequency will cause a change in phase relationship between the two voltages, and thus cause a change in control electrode bias of the auxiliary control tube 39. If the voltage from the 60 cycle multivibrator should tend to go above the frequency of the synchronizing source, the phase difference of the multivibration and synchronizing voltages is decreased, the rectified voltage across resistor 51 increased, thus causing a corresponding increase in auxiliary control tube impedance resulting in a corresponding change in the char acteristics of the coupling network, thus tending to slow the main oscillator tube frequency down to the proper amount so that the 60 cycle multivibrator voltage remains at a frequency equal to that of the synchronizing source.

While the invention has been disclosed in two of its preferred forms, it is obvious that changes in its general organization and arrangement may be made without departing from its true spirit I and scope, as set forth in the appended claims.

I claim as my invention:

1. In an oscillation generator, the combination of an electron discharge device having a cathode, an anode and a control electrode, an input circuit including said cathode and control electrode and an output circuit including said cathode and anode, a phase shifting network connected between said circuits and provided with an intermediate element, an auxiliary control tube including a cathode and anode and having an anode circuit including said intermediate element, a resistive element having a terminal maintained at a fixed potential, a second terminal of said resistive element connected to each of said cathodes, and means for varying the impedance of said control tube.

2. In an oscillation generator, the combination of an electron discharge device provided with input and output circuits, a filter network adapted to pass a wide band of frequencies connected between said circuits to cause a phase shift of voltage between said circuits and provided with an intermediate resistive element, an auxiliary-control tube connected to said intermediate element whereby said intermediate element is included in said control tube anode circuit, a cathode for said discharge device and said control device, a connection between said cathodes and a terminal of a resistive element having a second terminal maintained at a fixed potential, and means for varying the impedance of said control tube.

3. In an oscillation generator, the combination of an electron discharge device having an electron emissive cathode and provided with input and output circuits, a filter network provided with a point of fixed potential and adapted to pass a wide band of frequencies connected between said circuits to cause a substantially phase shift of voltage between said circuits, an intermediate element for said filter network including an auxiliary control tube whose cathode is connected to the cathode of said discharge device, a cathode resistor connected between said point of fixed potential and said cathodes, and means for changing the impedance of said control tube.

WALDEMAR J. POCH. 

